A fire expert explains why historic buildings like Notre-Dame Cathedral burn so easily

• • A fire ravaged the Notre-Dame Cathedral in Paris on Monday, knocking down its iconic spire.
  • Business Insider brought a fire expert into its studios, who explained that old buildings like the cathedral have several features that make them vulnerable to fire – especially during renovation.
  • Historic buildings are often filled or constructed with combustible materials, such as wood trusses. They also tend to lack fire walls and robust fire suppression systems.
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Following is a transcript of the video.

Christopher Marrion: When you start looking at fires in historic buildings, a number of common themes start to come through. One is looking at the combustible materials and the interior finishes and the overall structure being of combustible materials.

Then getting into potentially limited detection systems and being able to alert the emergency responders and delays with regards to that. Limits in terms of fire separations and compartmentation. Limited or even no automatic suppression system, such as sprinklers or water mist systems or anything like that, as well as then just giving them access to the site and being able to get close to the building and having the resources from water to having standpipes to having enclosed stairways that they can be working out of.

You know, taking one of those things out of that is challenging. But then when you kind of line all of these up together it creates a lot of challenges for firefighters to really, you know, be able to protect these buildings.

Hi, my name is Chris Marrion. I am a fire and disaster management consultant.

In terms of, yes, fires in historic buildings and structures, they are fairly common - not just in terms of there being a fire, but overall the extent of damage that then results once a fire does get started.

We've seen recently the Glasgow School of Art fire, the second fire there that was during restoration. We've seen it on a number of other buildings: Troitsky Cathedral in St. Petersburg, Wangdue Phodrang Dzong in Bhutan.

One part is just looking at the overall construction, in terms of the structural elements - the wood trusses, the roof decking, for instance, just regular interior finishes throughout these buildings that are a lot of times of wood.

When we first see some of these buildings they look like, you know, stone masonry-type construction that is non-combustible. Once going inside you can see a lot of times the interior finishes. A lot are covered in woodwork. The floors, the pews, and churches and so forth are all wood and combustible materials. And then over time, buildings continue to accumulate materials - papers, whether it's artwork, all types of different things that are actually combustible, and they just continue over time to build up and get placed throughout different areas of the building.

Some of the other things that we run into is just looking at fire separations, for instance. There may not be a fire separation. It may just be a large uncompartmented space that would allow the fire to spread within that space and to continue on kind of unchecked. They may have actually put in fire walls at times, but then over the years and centuries and so forth, you know, doors may be removed for various reasons.

One of the other things just to keep in mind too, you know, it's challenging to send emergency responders into those spaces. There's limited areas that they have to fight a fire from. They have limited water supplies and hoses and those types of things. So it's typically an externally fought fire. And when you look at that, you know, a lot of these roofs in these older buildings are of slate or a lead or copper or different types of materials, which are intended to keep the water out. So, you know, spraying water on the tops of these roofs, they're not actually, you know, penetrating into those upper attic spaces.

A lot of times when you do see fires in historic structures, it is a lot during restoration period. For instance, Troitsky Cathedral in Russia, several years ago there was a fire during construction. Wangdue Phodrang Dzong in Bhutan had a fire just a few years ago as well, too. There's a lot that's going on during that time that introduce hazards. We have, you know, a lot of temporary electrical, temporary lighting in those. We have hot works going on - cutting torches and welding operations and those types of things. So, you know, there's a fair amount of new ignition sources that are introduced there on a temporary basis.

We also can have a lot of combustible materials introduced to the site in terms of overall construction materials, potentially the scaffolding, those types of things that could be introduced on site. So in terms of the fire, the ignition potential could be increasing.

On the mitigation side, we often, you know the detection system maybe being installed or maybe covered over so that the dust and debris is creating nuisance alarms. And then on the fire separation side as well, too, at times, doors are taken off to be restored and they're bought somewhere else.

I think, you know, there's definitely things that can be done to help improve the protection of these buildings. I think, you know, over the years people have been living, working, you know, going to services in these buildings for years, and these buildings have lasted for centuries at times. And they're kind of gets this perception that, well we haven't had a fire and therefore we're safe and this is protected and we're okay. But you know, it really is just having an ignition source close to something that is combustible and just having that opportunity that something does ignite and has the opportunity to expand from there.

So just because it hasn't happened, doesn't mean that it is, you know, fireproof for instance. And I think we just need to remember that.